Free-breathing MRI with Self-Gating Motion Compensation
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Solution Overview
Problem
Conventional MRI methods for quantifying liver R2* relaxometry measurements under free-breathing conditions suffer from respiratory motion artifacts, which compromise quantification accuracy, especially in patient populations with breath-hold difficulties.
Innovation Solution
A free-breathing stack-of-radial MRI protocol with self-gating capability is employed, using gradient-delay-corrected radial readout views and inherent motion signals to compensate for respiratory motion, thereby generating motion-compensated multi-echo data for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Cartesian sampling MRI is used for liver PDFF and R2* measurements, then measurement precision is improved, but breath-holding is required which reduces ease of operation for certain patient populations
Solution Approach 1:
The k-space sampling is segmented into multiple radial trajectories that are acquired sequentially during free-breathing. Each radial trajectory samples a different angular orientation, and the complete set of radial samples is reconstructed to form the final image. This segmentation allows the acquisition to be distributed over multiple breath cycles rather than requiring a single prolonged breath-hold.
Solution Approach 2:
The patent employs dynamic radial sampling where the readout trajectory continuously rotates through different angular orientations during the acquisition. This dynamic approach allows the MRI scan to capture data throughout the respiratory cycle, making the acquisition robust to respiratory motion while eliminating the need for breath-holding. The radial readout orientation changes dynamically to sample k-space from multiple angles.
2Ease of operation
If free-breathing stack-of-radial imaging is used, then ease of operation is improved, but respiratory motion artifacts worsen R2* quantification accuracy
Solution Approach 1:
A self-gating signal is introduced as an intermediary to mediate between the respiratory motion and the R2* quantification. This signal is extracted from the MRI data itself (typically from the center of k-space or from a reference region) and represents the respiratory cycle. The R2* calculation is then corrected by referencing this gating signal, allowing the system to distinguish between signal changes due to respiration and those due to actual iron content variations.
Solution Approach 2:
The patent implements a feedback mechanism where the self-gating signal is used to retrospectively sort or correct the radial data based on the respiratory phase at the time of acquisition. This feedback allows the system to identify and correct for motion-induced errors in the R2* measurement by comparing the acquired data against the reference respiratory signal, thereby improving quantification accuracy despite free-breathing conditions.
3Manufacturing precision
If gradient delay correction is applied, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
Gradient delay correction is performed as a preliminary step before the main R2* quantification. The gradient delays are measured and corrected in advance, allowing the subsequent R2* calculation to proceed with already-corrected data. This preliminary action simplifies the overall process by separating the correction step from the quantification step, reducing the complexity of the main algorithm while maintaining high precision.
Data Source
AI summary
A method for acquiring magnetic resonance imaging data with respiratory motion compensation using one or more motion signals includes acquiring a plurality of gradient-delay-corrected radial readout views of a subject using a free-breathing multi-echo pulse sequence, and sampling a plurality of data points of the gradient-delay-corrected radial readout views to yield a self-gating signal. The self-gating signal is used to determine a plurality of respiratory motion states corresponding to the plurality of gradient-delay-corrected radial readout views. The respiratory motion states are used to correct respiratory motion bias in the gradient-delay-corrected radial readout views, thereby yielding gradient-delay-corrected and motion-compensated multi-echo data. One or more images are reconstructed using the gradient-delay-corrected and motion-compensated multi-echo data.